diff --git a/src/crystal/system/unix/signal.cr b/src/crystal/system/unix/signal.cr
index 26f4bf6cf7e9..12804ea00267 100644
--- a/src/crystal/system/unix/signal.cr
+++ b/src/crystal/system/unix/signal.cr
@@ -32,7 +32,7 @@ module Crystal::System::Signal
           action.sa_flags = LibC::SA_RESTART
 
           action.sa_sigaction = LibC::SigactionHandlerT.new do |value, _, _|
-            writer.write_bytes(value) unless writer.closed?
+            FileDescriptor.write_fully(writer.fd, pointerof(value)) unless writer.closed?
           end
           LibC.sigemptyset(pointerof(action.@sa_mask))
           LibC.sigaction(signal, pointerof(action), nil)